I found a note on usage of the word "couple" at this site: https://www.wordreference.com/definition/couple The note states: In referring to two people, "couple", like many collective nouns, may take either a singular or a plural verb. Most commonly, it is construed as a plural: "The couple were travelling to Texas." Based on this usage, I expect that some native speakers will prefer "the young couple WAS heading to California" and that other native speakers will prefer "the young couple WERE heading to California". The usage note claims that collective nouns may take either a singular or a plural verb. This statement is true, but there are regional differences. I'm from the US: in my experience most (but not all) collective nouns that name particular groups of people, such as "team", "band", "orchestra", "group", "chorus", "choir", "staff", "organization", and so on, always take a singular verb. However, in the UK and some other countries many of these words always take a plural verb.

A couple is an example of a collective noun. In your example, sentence 1 is correct. It is somewhat similar to the "team". You can’t have a team without individual members; even so, we discuss a team as a single entity. But the collective nouns can have a PLURAL verb depending on a situation. example: There are three teenagers in the living room . Are they all doing the same thing at once? Not likely! One is watching TV intently. Another is reading a book. The third has one eye on his computer. There is a single group of teenagers, but the members of the group are doing different things. Members of collective nouns can act the same way, as individuals doing their own thing. When members of a collective noun act as individuals, that collective noun is plural and must be paired with plural pronouns and plural verbs. So in your example, the couple was doing the same thing at once which was "HEADING". hope this one helps you.

Thanks, Eric.

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I agree this is confusing! But it is a singular noun so you should use singular verbs. If it is more than one couple or couples you can use were, but for a couple use was.